Process for electrodepositing lead dioxide



United States Patent PROCESS FOR ELECTRODEPOSITING LEAD DIOXIDE Linwood P. Morrison, Thomas A. Hale, and George W.

Parker, Rochester, N.Y., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy No Drawing. Filed Mar. 7, 1958, Ser. No. 719,983

6 Claims. (Cl. 204-57) This invention relates to electroplating and more particularly to an improved solution and process for electroplating lead dioxide onto electrical conducting metal surfaces which present a passive surface for lead dioxide. Such surfaces include various types of stainless steel, nickel, nickel alloys and platinum metals.

Heretofore in plating lead dioxide onto such passive metallic surfaces from aqueous electrolytic solutions of lead nitrate, it was found that the anode efficiency declined rather rapidly from an initial high of 95 to 100% to a lower range of 20 to 30% as the electroplating is continued. This decided drop in efliciency occurs even though the usual additions are made to control the pH, the metal content and the nitrate radical content of the plating bath. It is, therefore, quite apparent that such a large decline in plating efficiency seriously reduces production.

An object of the present invention is, therefore, to provide an improved process for maintaining or restoring the electroplating efficiency of a lead dioxide plating bath.

Another object of this invention is to provide an improved process for plating lead and dioxide coatings onto metals and alloys which have a passive surface.

A particular object of this invention is to provide an improved process for plating lead dioxide onto stainless steel.

Still another object is to provide an improved aqueous electroplating bath composition for the efficient plating of lead dioxide onto passive metallic surfaces.

Other objects will appear hereinafter.

We have discovered in accordance with the present invention that the efficiency of a lead dioxide plating solution may be maintained or restored by adding thereto an optimum amount of hydrogen peroxide.

In plating lead dioxide onto a passive metal surface an aqueous plating bath containing from to 65 oz./ gal. of lead nitrate, having an analysis of Pb++ of 3-40 oz./gal., of N0 2-25 oz./gal., and a pH of 1.5-6.0 may be effectively employed at a temperature of 120 to 190 F. with a current density of 100 to 300 amperes per square foot of anode area. The plating efiiciency of such baths will decline on continuing use. The anode efficiency drops so that with the same current density less lead dioxide will be deposited. This lowering of plating efiiciency appears to be caused by an increase of sodium nitrite in the bath. It has been found that the increase of 0.1% of sodium nitrite (NaNO will decrease the eificiency of the bath to 30% of the theoretical for plating of any lead dioxide. The term anode eificiency is that percentage of metal oxide deposited at the anode calculated from the amount which will theoretically form at the anode using Faradays Law of Electrochemistry.

We have found that lead dioxide plating solutions such as described above can be resolved to or maintained at effective efficiency by the additions of hydrogen peroxide. The amount of hydrogen peroxide that is added to the plating bath can be calculated by determining the plating efiiciency of the solution. We have found in employing a 300 gallon plating bath satisfactory efficiency limits are 85 to 87% of the theoretical. Hourly checks on the solution efficiency are made and if the efiiciency falls below 85% 500 cc. of 35% hydrogen peroxide are gradually 2,994,649 Patented Aug. 1, 1961 added over a half-hour period to raise the plating etfi-'- An electroplating bath having a volume of 300 gallons and containing 48 oz./ gal. of lead nitrate was employedj The anodes upon which the lead dioxide was plated were made of 18% chromium, 8% nickel stainless steel. A'

cathode of the same stainless steel was employed. The pH of the bath was 4.0. The bath was heated at F. A current density of amperes per square foot of anode was employed. In this 300 gallon bath a current. etficiency of 87% is satisfactory for commercial production. bath have been found satisfactory for general operation, the lead nitrate being replaced in accordance with the amount of lead dioxide being plated out of the bath. The pH maybe adjusted by adding lead salts such as lithar'ge (lead oxide) or white lead (basic lead carbonate). Hourly checks on the anode efficiency are also made. When employing this solution the anode efiiciency can be main tained by the additions of hydrogen peroxide, as indicated by the hourly inspection. If the efficiency of the bath falls to less than 85%, 500 cc. of 35% hydrogen peroxide solution are added slowly over a half-hour period of time. This will restore the anode efliciency. Without this hydrogen peroxide addition the anode efiiciency of the solution on prolonged use may eventually fall to 20 or 30%.

Example 2 The plating process described in Example 1 was repeated employing a plating bath containing 5 oz./gal. of lead nitrate (analysis Pb++ of 3 oz./gal.) (analysis N0, of 2 oz./gal.) a pH of 1.5, at a temperature of 120 F. with a current density of 100 amperes per square foot of anode area. The efiiciency of the bath was maintained above 85% by periodic additions of a 35 solution of hydrogen peroxide.

Example 3 The plating process described in Example 1 was repeated employing a plating bath containing 65 oz./ gal. of lead nitrate (analysis of Pb++ of 40 oz./gal.) (analysis of N0 of 25 oz./gal.) a pH of 5.0, at a temperature of F. with a current density of 300 amperes per square foot of anode area. The efliciency of this bath was maintained above 85 by periodic additions of a 35% solution of hydrogen peroxide.

The processes of Examples 1, 2 and 3 were employed to plate efficiently lead dioxide on 18-8 stainless steel; AISI 302 and 304; chromium stainless AISI 416 and 430 and each of the following nickel plated, low carbon steels: AISI C-l008; C-1010; C-10l2.

Our plating process is particularly advantageous for use in plating continuous strips of the above specified metals or alloys. The continuous strip of metal is made the anode and drawn throught the solution at a suitable rate, and a cathode is immersed in the bath. Of course, small metal plates or other metal surfaces can be held in the bath instead of being drawn therethrough.

Our process is, in fact, useful for plating lead dioxide upon any electrical conductor which has a passive surface for the lead dioxide such as stainless steel, nickel, nickel alloys and platinum metals. Our process has been effectively employed to plate certain types of energizer electrodes for electronic equipment.

We claim:

1. The method of plating lead dioxide upon a passive metal surface which comprises making the passive surface the anode in a plating bath containing 5 to 65 oz./ gal. of lead nitrate, maintaining the temperature of the bath Hourly checks on the composition and pH of the 3 within the range of from 120 to 190 F., maintaining the pH of the bath within the range of 1.5 to 6.0, passing the current within the range of 100 to 300 amperes per square v foot of anodesurface through said bath, and adding hydrogen peroxide thereto to maintain theanode efficiency of the bath above 85% p 2. The method of plating lead dioxide upon a passive metal surface which comprises making the passive surface the anode in a plating bath containing 48 oz./gal. of lead nitrate, said bath having a pH of 4 and a temperature of 150 F., passing a current of 175 amperes per square foot of passive surface through said bath, and adding hydrogen peroxide to the bath to maintain the anode efficiency of the bath above 85 E 3. The method of plating lead dioxide upon a passive stainless steel surface which comprises making the passive surface the anode in an aqueous plating bath containing 48 oz./gal. of lead nitrate, said bath having a pH of 4 and a temperature of 150 F., passing a current of 175 amperes per square foot of passive surface through said bath, and adding hydrogen peroxide to the bath to maintain the anode efiiciency above 85%.

4. The method of plating lead dioxide upon a passive nickel surface which comprises making the passive surface the anode in an aqueous plating bath containing 48 oz./ gal. of lead nitrate, said bath having a pH of 4 and a temperature of 150 F., passing a current of 175 amperes 4 per square foot of passive surface through said bath, and adding hydrogen peroxide to the bath to maintain the anode efliciency above 5. The method of plating lead dioxide upon a passive platinum surface which comprises making the passive surface the anode in an aqueous plating bath containing 48 oz./gal. of lead nitrate, said bath having a pH of 4 and a temperature of F., passing a current of amp eres per square foot of passive surface through said bath, and adding hydrogen peroxide to the bath to maintain the anode efficiency above 85% 6. The method of plating lead dioxide upon a passive nickel plated steel surface which comprises making the passive surface the anode in an aqueous plating bath containing 48.oz.'/gal. of lead nitrate, said bath having a pH of 4 and a temperature of 150 F., passing a current of 175 amperes per square foot of passive surface through said bath, and adding hydrogen peroxide to the bath to maintain the anode efliciency above 85%.

References Cited in the file of this patent UNITED STATES PATENTS 514,523 Canada July 12, 1955 

1. THE METHOD OF PLATING LEAD DIOXIDE UPON A PASSIVE METAL SURFACE WHICH COMPRISES MAKING THE PASSIVE SURFACE THE ANODE IN A PLATING BATH CONTAINING 5 TO 65 OZ./GAL, OF LEAD NITRATE, MAINTAINING THE TEMPERATURE OF THE BATH WITHIN THE RANGE OF FROM 120 TO 190*F., MAINTAINING THE PH OF THE BATH WITHIN THE RANGE OF 1.5 TO 6.0, PASSING THE CURRENT WITHIN THE RANGE OF 100 TO 300 AMPERES SQUARE FOOT OF ANODE SURFACE THROUGH SAID BATH, AND ADDING HYDROGEN PEROXIDE THERETO TO MAINTAIN THE ANODE EFFICIENCY OF THE BATH ABOVE 85%. 